Aircraft typically include at least one cargo compartment to transport goods and FAA regulations require that smoke detection systems be included in the aircraft to determine if smoke and/or fire are present in such cargo compartments. Smoke detection systems in aircraft cargo compartments have historically experienced a high incidence of false alarm rates. Some smoke detection systems used in aircraft cargo compartments consist of a network of “spot-type” particle sensor smoke detectors coupled with an alarm system. When particles are detected, the network of detectors sends alarm status signals to the alarm system, which provides a warning signal to the flight deck, where a decision may take place to initiate fire suppression and other safety systems. Other proposed smoke detection systems may employ video cameras.
The existence of particulates such as mist, dust, condensation, oil droplets and other aerosols in the cargo hold compartments and the sensitivity of current sensor systems contribute to the high false alarm rates. In some cases, the ratio of false to genuine alarms may reach 200:1. One study of verified smoke events vs. total alarms indicates that over 90% of all alarms are false due to these particulates. The direct cost of each false alarm can be very costly and may include indirect consequences such as (1) increased safety risk due to forced landings at unfamiliar or less adequate airports, (2) loss of confidence in detection systems, and (3) risk of injury to passengers and crewmembers during evacuation.
One approach to reducing false alarms has been to use a multi-sensor smoke detector package. For example, a joint project sponsored by the European Union produced such a system that includes four different types of sensors, two gas sensors, a particle sensor and a thermal sensor, in one package. In another example, NASA developed a new fire detector designed for significantly reducing the rate of false alarms aboard in cargo bay of aircraft. NASA's detection package includes miniaturized carbon monoxide and carbon dioxide sensors as well as a smoke particle sensor. The European Union and NASA multi-sensor smoke detector packages have similar approaches and should be able to effectively recognize a real fire in cargo bay. However, such systems are mounted within a package having a relatively large volume and heavy weight, and, in view of the large open space on a cargo bay in a wide body airplane, it may be difficult or impractical to place a large number of these sensor packages on the cargo bay ceiling. When multi-sensor smoke detector packages are distributed on a wide body airplane cargo bay ceiling, a resulting white space exists between each of the multi-sensor smoke detector packages. As evident, if a fire starts at an area adjacent to a portion of the white space farthest from any of the multi-sensor smoke detector packages, it will take much longer to detect than if it started directly adjacent to one of the multi-sensor smoke detector packages. As a result that there may be large open spaces on the cargo bay ceiling of the wide body airplane that are not covered by such sensors which could result in the failure to promptly identify some cargo fire events that start within the uncovered areas. In other words, if a fire starts at an area adjacent to a portion of the white space farthest from any of the multi-sensor smoke detector packages, it will take much longer to detect than if it started directly adjacent to one of the multi-sensor smoke detector packages. Other multi-sensor-based systems may face the same drawbacks.
Accordingly, a need exists in the art for improved techniques for smoke and fire hazard detection and evaluation.